This invention relates to a liner hanger for oil well completions, and more particularly, to a new and improved liner hanger for use in oil well completions which employs spiral slip means disposed along the length of the hanger body and complementary arranged for selective setting of the slip means in a well pipe.
In the drilling of oil wells, it is common practice to cement a tubular casing in the upper section of a drilled bore hole, the casing sometimes being referred to as "surface casing". After cementing the surface casing, the hole is again drilled for a suitable interval of depth and another casing typically is cemented in place. Successive intervals of depth in the well bore are drilled and cased and each such successive interval decreases in diametral size as a function of depth. In the use of pipe liners, a string of pipe is lowered into the drilled well bore to place the pipe in position. Then, the upper end of the string of pipe is anchored or supported at the lower end of the adjacent string of casing. The liner hanger at the upper end of the string of pipe has a supporting device which, when set, anchors and supports the depending string of pipe. It is obvious that such an anchoring and supporting device must support the substantial weight of the string of pipe depending below it. The depending string of pipe is sometimes limited in length to the weight of pipe that the anchoring and supporting device can support.
Typically, the anchoring and supporting device for a liner hanger consists of a tapered cone or cam surface with circumferentially spaced slip devices which are spaced from one another equidistantly around the circumference of the hanger body. To anchor the device, the slips and cones are moved longitudinally relative to one another from an "unset" condition to a "set" condition. The tapered cones cause the slips to be moved radially outwardly into anchoring engagement with the inner surface of the interior of the pipe casing. The outer surfaces of the slip have serrated or wickered surfaces which provide gripping engagement surfaces. Generally, either the tapered cone or the slips are attached to a tubular sleeve member which is slidably mounted on a body member. The sleeve device has external friction means for engaging the inner wall of the casing and a releasable locking device is provided between the sleeve member and body member which retains the slips and cones in an unset condition.
upon release of the locking device, the body member can move longitudinally relative to the friction means and the relative motion permits movement of the slips and cones to the set condition.
Typical types of mechanically set liners are illustrated in the composite catalog of Oilfield Equipment and Services, 33rd Revision 1978-1979, published by World Oil on pages 1062-1064 or page 6432. Other liner hangers which are set by hydraulic devices (which are commonly referred to as hydraulic set liner hangers) are described on pages 1062, 1074 and 6431 of the above described composite catalog.
It is extremely desirable and many times, necessary, in the design of a liner hanger to have the outer diameter of the hanger close as possible to the wall of the pipe. In other words, small clearances are necessary. For example, a 4 inch O.D. liner pipe is sized for passage through a 51/2 O.D. casing, or a 51/2 inch O.D. liner pipe is sized for passage through a 7 inch O.D. casing, or 75/8 O.D. liner pipe is sized for passage through a 95/8 inch O.D. casing. Where there is a minimal annular clearance space (or bypass area) between the outer surface of the liner hanger assembly and the inner surface of the pipe, it is difficult to pass the assembly through the fluids in the pipe because of the hydraulic effect which is produced. When the bypass area or clearance space between the liner hanger assembly and a string of pipe is restricted or limited, a number of things can happen when the liner hanger assembly is run through the casing. For example, pressure build-up below the hanger assembly can cause formation fracturing. Breakdown pressure gradients can be exceeded which result in lost circulation of fluids from the well bore. Where cement is involved, a restricted bypass area can cause premature gelling of cement if there is a slowdown in the circulation of the cement.
Prior attempts to solve liner hanger design problems involve, for example, the idea of creating narrow vertical spaces between adjacent cone segments and slips disposed about the circumference of a body member. Some solutions suggest providing vertical grooves or cuts vertically through an annular cone. It has also been suggested to vertically stagger sets of cone and slips along the length of a hanger assembly so that a multiple number of slips can be used for support of the pipe. Also, it has been suggested that vertically fluted or grooved cone surfaces be provided so that fluid is required to pass through narrow vertical channels.
In construction, sometimes the cones have been welded on the body of the pipe which will cause "hot spots". That is, the metalurgical characteristics of the pipe at the weld location are adversely affected. Where multiple, vertically staggered slip units are used, there is a lack of symmetry between the units so that uneven stress distributions occur in the units upon setting of the slips. Stress distributions can cause parts of the slip units to break off, and even cause the liner to fail and perhaps drop to the bottom of the well bore.